Are EnumMaps in Java perfect hash maps?

Question

If the list of hash keys for a hash function is known and immutable, it is possible to generate a perfect hash function. A Enum in Java is a list of known and immutable elements. Therefor it should be possible to implement the EnumMap as a perfect hash. Is this currently (1.7) done in Java?

Answer 1

No. EnumMap doesn't use hashing. It uses the enum ordinal values as indexes into an array of the value type.

Reference:

• http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/7-b147/java/util/EnumMap.java#EnumMap.getKeyUniverse%28java.lang.Class%29. (If this link breaks, Google for "java.util.EnumMap source".)